# What is a Reverse DNS (PTR) Record and Why Is It Mandatory?

https://bihostnet.com/en/knowledgebase/article/what-is-reverse-dns-rdns-ptr-record-guide

## Forward DNS vs Reverse DNS (PTR)

Standard A records resolve domain names to IP addresses. Reverse DNS (rDNS) performs the reciprocal lookup: querying an IP address to resolve its canonical hostname via a PTR (Pointer) record.

## Why Major Providers Reject Missing PTR Records

Mail transfer agents (Google, Microsoft, Yahoo) verify inbound connections against PTR records. If an IP lacks valid rDNS matching its HELO banner:

- Inbound mail is outright rejected with 550 5.7.1 error codes.
- Surviving messages are routed straight to Junk folders.

## Configuring PTR Records at BiHostNet

PTR records can only be configured by the entity controlling the subnet. Open a ticket via the BiHostNet Client Area specifying your IP and desired hostname (e.g., `mail.yourdomain.com`), and our network engineers will set it up promptly.